FIGS. 1 and 2 are a vertical sectional view and a side elevational view, respectively, showing this kind of conventional ignition coil. In the diagrams, reference numeral 1 denotes an iron core and 2 indicates a primary coil portion arranged around the outer periphery of the iron core 1. The primary coil portion 2 comprises a cylindrical bobbin portion 2a made of a resin and a primary winding 2b wound around the outer periphery of the bobbin portion 2a. Reference numeral 3 denotes a secondary coil portion arranged around the outer periphery of the primary coil portion 2. The secondary coil portion 3 comprises a cylindrical bobbin portion 3a made of a resin and a secondary winding 3c wound in a winding groove 3b formed in the outer periphery of the bobbin portion 3a. Reference numeral 4 denotes a pin-shaped high voltage terminal. The end of the secondary winding 3c is connected to a head portion 4a of the terminal 4. Reference numeral 5 denotes a casing made of a synthetic resin. The casing 5 comprises a hole portion 5a into which a high voltage cord (not shown) is inserted, and a casing main body portion 5b which encloses the iron core 1, primary coil portion 2 and secondary coil portion 3. Reference numeral 6 denotes a thermosetting resin which is injected in a liquid state into the casing main body portion 5b and is then hardened, thereby insulatively fixing the primary coil portion 2, secondary coil portion 3 and the like in the casing 5. Reference numerals 7a and 7b denote a power source side lead wire and a ground side lead wire, respectively, which consist of coated electric wires that penetrate the rear edge portion of the primary bobbin 2a. These lead wires 7a and 7b are connected to the primary winding 2b by soldering and are fixed in the casing 5 by the thermosetting resin 6. Thus, a transformer is constituted by laminating the iron core 1, primary coil portion 2 and secondary coil portion 3. The beginning of the primary winding 2b is connected to the ground side lead wire 7b. The end of the primary winding 2b and the beginning of the secondary winding 3c are connected to the power source side lead wire 7a. On the other hand, in order to connect an end 3d of the secondary winding 3c to a high voltage cord (not shown), the winding end 3d is connected by means of soldering to the head portion 4a of the high voltage terminal 4 which is previously press-inserted into the casing 5 by making use of a space 8 in the casing main body portion 5b. After the windings 2b and 3c, lead wires 7a and 7b and high voltage terminal 4 have been connected by way of soldering, the casing 5 is filled with the thermosetting resin 6.
A conventional ignition coil for internal combustion engines is constituted in the manner described above. Hence, after the secondary coil portion 3 has been inserted into the casing 5, the end 3d of the secondary winding 3c in the secondary coil portion 3 needs to be soldered to the head portion 4a of the high voltage terminal 4. Consequently, the space portion 8 needs to be formed to allow the soldering work to be performed. This raises the problem that the overall size of the ignition coil becomes relatively large. On the other hand, since the distance from an opening 5c of the casing 5 to the head portion 4a of the high voltage terminal 4 is fairly great, there is also a problem in that the soldering work is difficult and the productivity of a mass production process therefore suffers.
The present invention has been achieved with a view to solving the foregoing problems and it is an object of the invention to obtain an ignition coil for use in internal combustion engines which can be miniaturized and offers high productivity gains when applied to a mass production process.